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Evolutionary Demography and how to die, or not

On Denmark’s island of microbreweries, I learnt how to avoid death.
This was the first meeting of the Evolutionary Demography Society, held in the city of Odense, a place aching to be described as quaint.

Biologists are fond of quoting the eminent early-20th Century geneticist Theodosius Dobzhansky, who once wrote: “Nothing in biology makes sense except in the light of evolution.” In Odense, we heard that nothing in evolution makes sense except in the light of demography.

Demography is the science of using statistics to study populations, human or not. In essence, populations change according to a basic equation of births – deaths + immigration – emigration. In reality, fertility, mortality and migration are messier processes, meaning demography is a little like accountancy crossed with fluid dynamics.

Evolutionary theory gives a frame on which to hang the processes of demography. Like demography, evolutionary sciences are concerned with fertility, mortality and migration: the flow of genes through space and time. Combining the two, we can scale up from genes to individuals to groups, communities and populations, and figure out how everything affects everything else. Broadly speaking, of course.

A cool feature of the meeting was the ‘lightning talks’ – giving researchers five minutes to present their work. Such rapid-fire science was, alas, a little overwhelming and what follows is only what my biased, selective, novelty-seeking memory can recall.

Over the three days, we heard a lot about senescence – growing old. The speakers served great reminders (especially since I keep forgetting this) that not everything will grow old and not everything is destined to necessarily die.

Hydra – a tiny, tubular, freshwater animal – contain stem cells that can regenerate the little dude over and over, at least under experimental conditions. In the wild, they can die through injury or disease which is why they haven’t (yet) taken over the world. But they seem to be biologically immortal.

Other animals such as certain species of tortoise as well as a bunch of plants may keep growing larger and more fertile as they age. The mortality for these so-called indeterminate-growth species goes down rather than up.

The more familiar pattern of senescence – that is, increasing risk of death as you get older – may not be quite what we expected either. At extreme ages, say humans over 110 years old, the risk of dying may level off. At this point it’s not all peachy: there is still a 50-50 chance of death with each passing year but the point is that the risk plateaus: it doesn’t keep going up.

There was much, much, MUCH more and the organisers thankfully recorded all talks, so I’ll post links as and when they become available.

My talk was a side-project I spent a lot of last year working on (and was originally my PhD topic). It’s a model that looks at the situations under which humans can shorten or space out the time between babies, depending on their risk of dying and their children’s risks of dying.